1. Field of the Invention
This invention relates to a gene coding for Pin m III which is associated with overwintering and frost hardiness of western white pine.
The invention also relates to a method of determining the frost hardiness of a conifer seedling, and to a method for determining the susceptibility of conifers to blister rust fungus.
2. Description of the Prior Art
The following disclosure refers to a plurality of literature references. The references are listed numerically at the end of this disclosure
White pine blister rust is a disease of five-needle pines, e.g. western white pine (Pinus monticola D. Don), eastern white pine (Pinus strobes L.) and sugar pine (Pinus lambertiana Dougl.), caused by the blister rust fungus, Cronartium ribicola Fisch. The fungus has five different spore stages on two unrelated hosts, white pines and Ribes species. The basidiospores are produced on Ribes in the fall and transported by wind to pine foliage, where they germinate and infect the needle via stomata and produce infection spot. Hyphae grow down the needle into the bark, causing a perennial canker which eventually kills the tree. Although some large and older trees can survive, infected younger trees almost inevitably die. We have been studying proteins involved in this host-pathogen interaction. (e.g. Ekramoddoullah and Hunt, 1993, Ref. 10). During this investigation it was observed that environmental factors also contributed to the changes in the synthesis of proteins. Plants presumably respond to signals generated by environmental stresses, e.g. low and high temperature, photoperiod, drought, salinity and are capable of responding to a varying degree to the stresses (Bohnert et al., 1995, Ref. 3). Plants also are continually exposed to numerous microorganisms but are susceptible only to a few of them. In response to both abiotic and biotic stresses, induction of several proteins in plants have been identified (Heikila et al., 1984, Ref. 16; Ort et al., 1989, Ref. 32; Hightower, 1991, Ref. 17; Stintzi et al., 1993, Ref. 41; Ekramoddoullah et al., 1995, Ref. 12; Sabehat et al., 1996, Ref. 37; Mauch et al. 1988, Ref. 28). Although functions for many of these proteins have not yet been assigned, accumulation of a group of proteins termed "pathogenesis-related" proteins (van Loon, 1985, Ref. 48; Linthorst, 1991, Ref. 25) is considered an important feature of plant defence response upon infection. Some of these proteins could be induced by either abiotic or biotic stress. For example, a protein osmotin that accumulates during adaptation of tobacco cells to osmotic stress could be induced in tobacco leaves infected with tobacco mosaic virus (Stintzi et al., 1991, Ref. 40). Genes encoding vegetative storage proteins were expressed following wounding and water deficit (Mason et al., 1991, Ref. 27). A major protein, sporamin of potato tuberous roots (Maeshima et al., 1985, Ref. 26), which is developmentally regulated, could be induced in petioles by treatment with fungal elicitors, polygalacturonic acid and chitosan (Ohto et al., 1992, Ref. 31). A family of wound induced genes in Populus shares common features with genes encoding vegetative storage proteins (Davis et al., 1993, Ref. 7) that also accumulate seasonally in poplar bark tissues (Clausen and Apel, 1991, Ref. 5)). A group of antifreeze like proteins in rye grass was shown to have amino acid sequence homology with pathogenesis-related proteins (Hon et al., 1995, Ref. 18). Recently, a sugar pine protein Pin l I was detected in the foliage in increasing amounts in the fall (Ekramoddoullah et al. 1995, Ref. 12). The homologue of this fall protein, named as Pin m III, was also identified in western white pine foliage. An 89% homology of the N-terminal amino acid sequence of Pin m III was found with Pin l I (Ekramoddoullah and Taylor, 1996, Ref. 13). The quantity of Pin m III in western white pine seedlings was shown to be seasonally regulated; increasing as fall progressed to a maximum in the winter months, and reducing to lowest levels in the summer months (Ekramoddoullah et al. 1995, Ref. 12). Pin m III has also been shown to be associated with frost hardiness of western white pine.